1. Field of the Invention
The present invention concerns torque measuring devices. More particularly, the present invention concerns devices that can measure torque as it is being applied to a joint, independent of the direction of fastening of the joint. Even more particularly, the present invention concerns devices that measure torque that is either being currently applied to a joint or that has been previously applied to the joint.
2. Description of the Prior Art
Heretofore, it has been desired, in fact required, to ensure that a pre-determined amount of torque be applied to a fastener. This occurs in many manufacturing applications, where the torque applied to a bolt or plurality of fasteners must be within set tolerances. Failure to maintain the torque applied within those values can result in improper joints being formed, with instability inherent therein. It therefore became desirable to test the torque previously applied to a joint after tightening had been effected.
One attempt to address this problem is found in U.S. Pat. Nos. 4,244,213 and 4,319,494 issued to Marcinkiewicz, and both of which are herein incorporated by reference. Marcinkiewicz teaches broadly the concept of recording the changes in the slope of the torque applied to a nut. The advantage in a system of this type is that it allows a testing of the torque previously applied to a joint, to ensure that the joint has the proper tension. Such testing is termed auditing or retorquing.
The devices of the Marcinkiewicz patents are especially set to observe the negative valley torque, which occurs after the breakaway. Marcinkiewicz utilized a microprocessor to record these values and display a resulting value. By this method, the joint effected can be tested without the need of unfastening the joint, which previously was the case. Unfortunately, spikes due to interference or operator error give false results, which can nullify the data recorded.
The problem associated electrical "spikes" which can disrupt data in such auditing instruments was partially addressed in U.S. Pat. No. 4,450,727, issued to Reinholm et alia and incorporated herein by reference. Reinholm et alia builds upon the prior art to control a window of readings for the device. The device of Reinholm measures the changes in the slope of two "endpoints" of the torque signal being applied to the nut. This allows the sensing of the breakaway torque by denoting a slope of a minimum value. When this value is achieved, the breakaway torque has been realized and the reading of signals is halted. This gives a purity to the data collected and a more accurate reading.
As helpful as these advances are, these devices are directed to the auditing of torque previously applied to a joint. There exists a need for a device that can accurately monitor the application of torque to a joint during the application thereof, a need that these devices do not address. Further, there is a need for a device that can both monitor the torque as it is being applied and is capable of auditing the torque after it has been applied.
There also exists a need in the art for a device that is capable of reading torque as it is being applied to a joint independent of the direction of fastening of the joint. There exist applications, such as the construction of fire extinguishers and some medical equipment, that have multiple joints, some of which are clockwise tightened joints and some being counter-clockwise tightened joints. There currently exists no device to either monitor the torque to joints of differing fastening direction, either as it is applied or after it has been applied, without altering and recalibrating the equipment. Thus, there is needed a device which, without alteration, may determine the torque applied to a fastener while either rotating clockwise or counter-clockwise.
It is to these needs that the present invention is directed.